A kind of method and etching liquid thereof at polyimide base material of flexible printed circuit board uplifting window mouth
Technical field
A kind of method and etching liquid thereof at polyimide base material of flexible printed circuit board uplifting window mouth belong to the material technology field, particularly the flexible printed-circuit board process technology.
Background technology
Flexible printed-circuit board is normally a kind of to be the printed circuit board of base material with polyimides (PI), flexible printed-circuit board has three layers (single sided boards) or five layers of (double sided board) structure usually, as shown in Figure 1, 2, wherein, 1 is the PI substrate layer, 2 is copper foil layer (circuit layer), and 3 is the adhesive linkage of acrylic compounds; Now also have or not the flexible printed-circuit board of acrylic compounds adhesive linkage, this flexible printed-circuit board is the structure of two-layer (single sided board) or three layers (double sided boards).The thickness of entire circuit plate is about several millimeters at zero point.Usually, on the circuit layer of the flexible printed-circuit board of carrying out physical circuit, also have one deck PI encapsulated layer, be scratched to avoid electric short circuit or circuit layer.The characteristics of flexible printed-circuit board maximum have flexible exactly, can be crooked easily, and the interconnection and the many data interface circuits that are particularly suitable between the multilayer rigid circuit board are used.At present, flexible printed-circuit board is used widely in the middle of many electronic equipments such as mobile phone, digital camera, video camera, notebook computer, avionic device.
Often need leave the window of designing requirement size in the flexible printed-circuit board production in specific zone.Two flexible FPC window board as shown in Figure 1, leave the window of pre-sizing in the zone that indicates, on the basis of individual layer, realize the function of double-side conduction, and because the hollow out place does not have PI, has only one deck Copper Foil, do not have PI, its resistance to elevated temperatures is irrelevant with PI, so have good resistance to elevated temperatures when welding.
Existing method at the specific regional windowing of flexible printed-circuit board mainly contains machining and chemical etching two big classes.Wherein machining has again that machinery is die-cut, numerical control is milled etc.; Chemical etching has plasma etching, laser ablation etc.
● machinery is die-cut
The punch press that the die-cut main employing of machinery is 20 tons uses mould to carry out die-cut.The advantage of this technology has: production lot is big, and input cost is low in advance, and the production consuming cost is low; Shortcoming mainly is: owing to be subjected to the restriction of punch die precision, processing precision of products is low, and window size is more little, and die needed cost is just high more, produces just difficult more.
● numerical control is milled
The equipment that employing is milled in control is single shaft or multi-axis numerical control milling machine, cooperates the carbide-tipped milling cutter of various sizes to process.Be characterized in: with short production cycle, in batches big, machining accuracy is moderate, input cost height in advance, and the production consuming cost is low.But for the production of flexible printed board, since base material quality softness, the rigidity deficiency, and processing often produces a large amount of burrs at the edge of window afterwards, or even tears the situation of distortion.Be not suitable for now to the miniaturization that flex plate proposed highdensity requirement.
● plasma etching
Plasma etching adopts special production equipment, adds different reacting gass at different base materials and grows.This explained hereafter is little in batches, drops into and maintenance cost high the machining accuracy height in advance.
● laser ablation
That laser ablation mainly adopts is C0
2Infrared laser or UV laser etc.This technology almost is fit to all organic insulation base materials.The window precision height that is processed, but production lot is little, drops into and the maintenance cost height.Be not suitable for general middle-size and small-size flexible printed-circuit board enterprise.
For developing flexible printed board enterprise, select plasma etching and laser ablation not ideal, drop in advance and maintenance cost too high, and also high to operator's requirement.And adopt machinery die-cut, often can only be applied in some in the not high single or double flexible electric circuit board of required precision, thereby but can't finish production and development restriction company in the production of small-sized, the highdensity flexible electric circuit board of high added value.
Summary of the invention
Deficiency at existing the whole bag of tricks at the specific regional windowing of flexible printed-circuit board, the invention provides a kind of method and etching liquid thereof at polyimide base material of flexible printed circuit board uplifting window mouth, the side of its windowing sends out that technology is simple, efficient is high, precision is high, and its etching liquid prescription is simple, process for preparation simple and can get specific embodiment with its windowing combines.
A kind of method at polyimide base material uplifting window mouth may further comprise the steps:
1, preliminary treatment.Pre-treatment step mainly is to remove grease contamination possible on the flexible printed-circuit board and oxide layer and too much moisture, and specific practice is to carry out acid deoiling earlier, to remove grease contamination possible on the plate face and oxide layer; Washing oven dry again.
2, chemical etching pre-treatment.The chemical etching pre-treatment step mainly is not need the zone of windowing to protect to flexible printed-circuit board; specific practice is with through the two-sided diaphragm/glue that adds the anti-highly basic of last layer of pretreated flexible printed-circuit board, utilizes photoetching process to expose after exposure imaging to need windowing to get regional.
3, chemical etching.Chemical etch step mainly is to utilize chemical etching liquid to etch away the PI base material that flexible printed-circuit board needs the windowing zone, thereby leaves required window.Specific practice is to take out behind 100-120 ℃ of following reactive ion etching certain hours through the flexible printed-circuit board immersion chemical etching liquor of step 2 processing.
4, etching reprocessing.The etching post-processing step mainly is to remove a large amount of alkali lye that flexible printed-circuit board is taken out of after chemical etch step, avoids polluting step operation down; Handle through demoulding then, remove on the flexible printed-circuit board other protective layer; After washing, oven dry obtain holding successfully the flexible printed-circuit board of window.
In the step 1, can use the acid deoiling mode to remove grease contamination and oxide layer possible on the flexible printed-circuit board plate face, specific practice is to take out after flexible printed-circuit board is put into acid deoiling liquid (Op emulsifying agent+sulfuric acid) 2~6min; The process of washing oven dry can be utilized pressure roller to remove the most of moisture of plate face and then enter drying tunnel to dry.
For the diaphragm/glue of anti-highly basic in the step 2, what the present invention selected to use is the FX940 or the FX9420 dry film of Du Pont, and this type dry film can anti-within a certain period of time highly basic; And can be dissolved in NaOH (NaOH) solution of low concentration, the demoulding of being convenient in the step 4 is handled.For the flexible printed-circuit board of different PI thickness, adjust suitable pad pasting pressure and speed during pad pasting, the pad pasting of avoiding insufficient pressure or excessive velocities to cause is unreal, and the excessive or speed of pressure causes that excessively slowly the plate face curls etc.For the flexible printed-circuit board of different PI thickness, consider the length of disposing time simultaneously, can paste two-layer or the multilayer dry film.During exposure,, avoid liquid medicine attack lateral erosion that causes and the flexible printed-circuit board dilatancy of losing excessively or high temperature causes, preferably adopt the mode of double-sided exposure, make that etching liquid can two-sided etching PI base material in order to shorten the processing time.
When carrying out the described chemical etching of step 3,, a plurality of flexible printed-circuit boards of windowing that need after step 1,2 can be immersed chemical etching liquor simultaneously, but should guarantee not phase adhesion between each flexible printed-circuit board in order to improve etching efficient; The reactive ion etching time, during reaction, flexible printed-circuit board gently vibrated between 3~5 minutes.
During step 4 etching reprocessing, the alkali lye that the mode flush away flush away of taking to wash is taken out of from etching bath guarantees not pollute liquid parting; During demoulding, will put into demoulding solution through the flexible printed-circuit board after etching, washing are handled and vibrate gently 1~3 minute, the concrete time decides on the number of plies of subsides dry film; After treating that dry film all dissolves, take out the washing oven dry.Demoulding solution is taked the strong base solution of low concentration, such as sodium hydroxide solution.
Need to prove, the present invention is to provide a kind of method of utilizing etching liquid at polyimide base material of flexible printed circuit board uplifting window mouth, belong to method for chemially etching; Etching liquid provided by the present invention is primarily aimed at is that the polyimide base material of flexible printed-circuit board carries out etching, this etching liquid is inoperative to copper and acrylic compounds adhesive linkage, if flexible printed-circuit board contains the acrylic compounds adhesive linkage, the local two-sided copper that all covered that perhaps needs windowing, need early stage technology to remove the acrylic compounds adhesive linkage earlier and need the copper at windowing position so, utilize etching liquid of the present invention that the PI base material is carried out etching again, thereby leave satisfactory window.
Chemical etching liquid described in the step 3, solute comprises: potassium hydroxide, NaOH, additive 1 or/and additive 2 or/and bleeding agent, solvent is a water, its prescription is: each rises the potassium hydroxide that solution contains the 530-630 gram, contain the NaOH of 30-45 gram, contain 25-45 milligrams additive 1 or/and contain 10-35 milligrams additive 2 or/and contain 2-6 milligrams bleeding agent.
Additive 1 in the prescription is a kind of corrosion inhibiter, can be BTA (BTA) and derivative 4-hydroxybenzotriazole (4CBTA) thereof, 5-hydroxybenzotriazole (5CBTA), CBT-1 (mixture of 4CBTA and 5CBTA), 1-[(1 '-imidazoles)-methyl] BTA (IMBTA), six methines, four ammonia etc.; Additive 2 also is a kind of corrosion inhibiter, can be that mercaptobenzothiazoler (MBT) and derivative 2-ethylmercapto group benzo thiazole thereof, 2-dibenzylsulfide are for benzothiazole, 2-octyl two sulfo-benzothiazoles etc.; Bleeding agent can be alkylphenol-polyethenoxy phosphate kalium salt, SAS (SAS), alkyl phosphate, uncommon sharp imperial FR-SD etc.
The preparation of etching solution there is no special feature, but need to prove, alkali is water-soluble to be exothermic reaction, solution temperature is about 100 degrees centigrade after mixed base dissolves fully, so the preparation and the described chemical etching of step 3 of etching liquid can be combined, to make full use of the heat that is produced in the process for preparation with etching liquid; In addition, because under the condition of thermokalite, exposed Copper Foil very easily is oxidized to Cu by the dissolved oxygen in the solution
2O is so add BTA and MBT compound corrosion inhibitor.
Chemical etching liquor etching reaction mechanism
1, etching solution etching polyimide base material mechanism
Flexible printed-circuit board is as follows with the general formula of insulating material:
Issue unboiled water in the effect of dense hot highly basic KOH and separate reaction, its reaction mechanism is as follows:
It at room temperature reacts carry out very slow, and is irreversible.The temperature that improves reaction system can greatly improve reaction speed.
2, corrosion inhibiter mechanism
The effect of the corrosion inhibiter in the prescription is in the etching process of etching liquid to the polyimide base material windowing, delays the corrosion thin to metallic copper on the base material.
BTA is a kind of corrosion inhibiter of effective copper, and its molecular structure is as follows:
When BTA contacted with copper and copper alloy, BTA produced chemisorbed on the metal surface.Lone pair electrons in the BTA molecule on the N atom link to each other with Cu with coordinate bond, and polymeric chain is connected by Cu atom at interval, thereby forms following structure:
The diaphragm that BTA generates on the copper surface is a multilayer film, and this film is a kind of two-dimensional polymer of chemisorbed, has linear structure, and it consists of Cu/CuzO/Cu (I) BTA.
BTA forms the corrosion that the complex compound film stops copper by the Cu on the copper surface, and this film-strength is big, and compactness is good, have good corrosion inhibition, but film forming speed is slow, if imperfect, can cause localized loss.And MBT stops the corrosion of copper by directly being adsorbed on copper surface, and adsorption rate is fast, generally can not cause localized loss.Therefore utilize the two different film forming procedure, when the two coexists as in the individual system, the interface interaction of mutually promoting forms polynary diaphragm and produces good adding and cooperative effect.
Above-mentioned etching solution prescription adopts composite corrosion inhibiter, and corrosion mitigating effect is better.
3, bleeding agent mechanism
Bleeding agent is that a class can make liquid be penetrated into the surfactant of certain solid interior quickly and evenly.
The alkylphenol-polyethenoxy phosphate kalium salt, right and wrong, anion surfactant have special structure, are inserted with the APEO of hydrophilic group between lipophilic group and ion head.Thereby has the particularity that is different from nonionic and anion surfactant.It is single, double ester admixture.Wherein dibasic acid esters molecules of salt structure is:
The monoester salt molecular structure is a di-potassium.
This material hydrophobic part is easy to form micella comparatively speaking and is difficult to surface adsorption for the long-chain straight chained alkyl of band phenyl ring in solution.It is in aqueous slkali, and alkali produces electrically anionicsite and to ion-atmosphere generation compression on the surfactant anion head, reduces interionic electron repelling, helps the surface to go up absorption and closely arrangement, and solution surface tension is reduced, and penetration increases.Thereby reach the purpose of quickening etching reaction, shorten the reaction time, reduce the dilatancy of Copper Foil.
In addition from considerations such as material performance, sources, the surfactant of single structure does not have performances such as good penetration, washing, emulsification, dispersiveness and high temperature resistant, alkaline-resisting, resistance to oxidation concurrently.Utilize alkaline-resisting, the heat resistance and the SAS excellent permeation of phosphate.Selecting sodium alkyl sulfonate and secondary alkyl phosphate is raw material.Reach above-mentioned effect by adjusting its component and type.
Advantage of the present invention:
1. the method economy at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention, easy, practical, quick and efficient, and can satisfy required precision.
2, the etching liquid that is used for etching flexible printed-circuit board polyimide base material of the present invention, its raw material economics, preparation and can combine with its etching process easily easily.
Description of drawings
Fig. 1: single face flexible printed-circuit board system structural representation, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer), and 3 is the adhesive linkage of acrylic compounds.
Fig. 2: double-faced flexible printed circuit board system structural representation, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer), and 3 is the adhesive linkage of acrylic compounds.。
Fig. 3: the pretreated flexible printed-circuit board structural representation that needs windowing, wherein, 1 is the PI substrate layer, 2 is copper foil layer (circuit layer).
Fig. 4: the flexible printed-circuit board structural representation of the need windowing behind the pad pasting, before the exposure, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer), and 4 is diaphragm.
Fig. 5: the flexible printed-circuit board structural representation of the need windowing after the development, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer), and 4 is diaphragm.
Fig. 6: the flexible printed-circuit board structural representation after the etching, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer), and 4 is diaphragm.
Fig. 7: hold the flexible printed-circuit board structural representation of window successfully, wherein, 1 is the PI substrate layer, and 2 is copper foil layer (circuit layer).
Fig. 8: the process chart of the method at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention.
Embodiment
Embodiment one
The preparation etching liquid
The KOH and the 6KgNaOH that take by weighing 106Kg add pure water to 200L, stir to make its dissolving.Because alkali is water-soluble to be exothermic reaction, when mixed base dissolves fully after solution temperature about 100 degrees centigrade, suitable heating stable temperature to 110 ℃ also.
Add additive 1, as BTA (BTA) 5kg and additive 2, as mercaptobenzothiazoler (MBT) 2kg, stirring makes it to dissolve fully.Add bleeding agent then, as alkylphenol-polyethenoxy phosphate kalium salt 800mg.
After etching liquid prepares, according to the method work flow operation at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention 4342w/A type FPC plate is processed, wherein, etch period is controlled at about 3 minutes and 30 seconds in the step 3, final the window of carving is neat, no lateral erosion, ooze the erosion situation, precision reaches designing requirement.
Embodiment two
The KOH and the 7.5KgNaOH that take by weighing 106Kg add pure water to 200L, stir to make its dissolving.Because alkali is water-soluble to be exothermic reaction, when mixed base dissolves fully after solution temperature about 100 degrees centigrade, suitable heating stable temperature to 110 ℃ also.
Add additive 1, as BTA (BTA) 7kg, stirring makes it to dissolve fully.Add bleeding agent then, as alkylphenol-polyethenoxy phosphate kalium salt 800mg.
After etching liquid prepares, according to the method work flow operation at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention 4342w/A type FPC plate is processed, wherein, etch period was controlled at about 3 minutes in the step 3, final the window of carving is neat, no lateral erosion, ooze the erosion situation, precision reaches designing requirement.
Embodiment three
The KOH and the 7.5KgNaOH that take by weighing 116Kg add pure water to 200L, stir to make its dissolving.Because alkali is water-soluble to be exothermic reaction, when mixed base dissolves fully after solution temperature about 100 degrees centigrade, suitable heating stable temperature to 110 ℃ also.
Add additive 1, as BTA (BTA) 5kg and additive 2, as mercaptobenzothiazoler (MBT) 4.5kg, stirring makes it to dissolve fully.
After etching liquid prepares, according to the method work flow operation at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention 4342w/A type FPC plate is processed, wherein, etch period is controlled at about 3 minutes and 10 seconds in the step 3, final the window of carving is neat, but have a little lateral erosion, ooze the erosion situation, precision reaches designing requirement.
Embodiment four
The KOH and the 7.5KgNaOH that take by weighing 126Kg add pure water to 200L, stir to make its dissolving.Because alkali is water-soluble to be exothermic reaction, when mixed base dissolves fully after solution temperature about 100 degrees centigrade, suitable heating stable temperature to 110 ℃ also.
Add additive 2, as mercaptobenzothiazoler (MBT) 4.5kg, stirring makes it to dissolve fully.Add bleeding agent then, as alkylphenol-polyethenoxy phosphate kalium salt 800mg.
After etching liquid prepares, according to the method work flow operation at polyimide base material of flexible printed circuit board uplifting window mouth of the present invention 4342w/A type FPC plate is processed, wherein, etch period is controlled at about 2 minutes and 50 seconds in the step 3, final the window of carving is neat, no lateral erosion, ooze the erosion situation, precision reaches designing requirement.